The editorial declares: "Today, Britain's three leading Jewish newspapers – Jewish Chronicle, Jewish News and Jewish Telegraph – take the unprecedented step of speaking as one by publishing the same front page.

"We do so because of the existential threat to Jewish life in this country that would be posed by a Jeremy Corbyn-led government.

Image: The papers say a Corbyn government would be a threat to Jewish life

"We do so because the party that was, until recently, the natural home for our community has seen its values and integrity eroded by Corbynite contempt for Jews and Israel."

Stephen Pollard, editor of the Jewish Chronicle, told Sky News that the front pages – on papers that normally have an "intense rivalry" – were unique and had been prompted by "Labour's anti-Semitism crisis".

Labour insisted in a statement that it "poses no threat of any kind whatsoever to Jewish people" and is "fully committed to the support, defence and celebration of the Jewish community and its organisations".

However, the party said it realised there "is a huge amount of work to do" to build trust with the Jewish community.

The editorial was published a little over 24 hours after the Parliamentary Labour Party put itself at odds with the party's ruling national executive by backing an emergency motion endorsing an internationally recognised definition of anti-Semitism.

The MPs' move came after the national executive, dominated by supporters of Mr Corbyn, agreed last week to amend and delete parts of the definition put forward by the International Holocaust Remembrance Alliance

0:25Video: Corbyn defends party's anti-Semitism code

Pulling no punches, the editorial in the papers continues: "The stain and shame of anti-Semitism has coursed through Her Majesty's Opposition since Jeremy Corbyn became leader in 2015.

"From Chakrabarti to Livingstone, there have been many alarming lows. Last week's stubborn refusal to adopt the full International Holocaust Remembrance Alliance's definition of anti-Semitism, provoking Labour MP Dame Margaret Hodge to call her leader an anti-Semite to his face, was the most sinister yet.

"Labour has diluted the IHRA definition, accepted in full by the government and more than 130 local councils, deleting and amending four key examples of anti-Semitism relating to Israel."

And the editorial claims: "Under its adapted guidelines, a Labour Party member is free to claim Israel's existence is a racist endeavour and compare Israeli policies to those of Nazi Germany, unless "intent" – whatever that means – can be proved. 'Dirty Jew' is wrong, 'Zionist bitch' fair game?

"The reason for this move? Had the full IHRA definition with examples relating to Israel been approved, hundreds, if not thousands, of Labour and Momentum members would need to be expelled."

The editorial concludes: "With the government in Brexit disarray, there is a clear and present danger that a man with a default blindness to the Jewish community's fears, a man who has a problem seeing that hateful rhetoric aimed at Israel can easily step into anti-Semitism, could be our next prime minister.

"Following that, it will face a binary choice: implement IHRA in full or be seen by all decent people as an institutionally racist, anti-Semitic party. After three deeply painful years for our community, September is finally make or break."

In response, Labour said its NEC had now "re-opened the development of the code, in consultation with Jewish community organisations and groups".

The party added that it had "concerns about one half of one of the IHRA's 11 examples, which could be used to deny Palestinians, including Palestinian citizens of Israel and their supporters, their rights and freedoms to describe the discrimination and injustices they face in the language they deem appropriate".

Responding to the editorial, Gideon Falter, chairman of Campaign Against Anti-Semitism, said: "We hear from members of our community constantly that were Jeremy Corbyn to become prime minister, they would take the drastic step of leaving the country.

"Some are making preparations already. Jeremy Corbyn has displayed utter contempt for the Jewish community that was so instrumental in building the Labour Party, as well as his own MPs who have begged him to take action against anti-Semitism.

Unprecedented and very upsetting. And fairly easy to begin resolving. Starting with the NEC accepting the IHRA definition. https://t.co/qY6vcIkqQ6

"In Britain in 2018, the once anti-racist Labour Party is now so institutionally anti-Semitic under Jeremy Corbyn that the Jewish community considers it to be a threat to our very future in this country."

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Some Labour MPs reacted with gloom and despair to the joint editorial.

Ana Turley tweeted: "Unprecedented and very upsetting. And fairly easy to begin resolving. Starting with the NEC accepting the IHRA definition."